The present invention relates to an alarm system, and more particularly to an alarm system that inhibits theft of articles by sensing and indicating unauthorized movement of an article.
A variety of different types of alarms have been developed in the past to protect against the theft of various articles. Once specific area in which theft is becoming an increasing concern is in the field of office equipment, particularly for items such as typewriters and other portable word processing equipment. Because of the increasing complexity and sophistication imparted to this type of equipment as a result of technological advances, and the concurrent increase in market value of these devices, as well as the readily available market for resale, the likelihood of theft is ever increasing. It is a general object of the present invention to provide a novel alarm system that is an effective and inexpensive deterrent to the unauthorized removal of an article, such as typewriter, from its proper location.
In the past, various approaches have been taken in an attempt to provide an effective means for producing an audible or visible alarm indication upon the attempted removal of an article. In one such approach, an electrically actuated, normally closed relay was placed in series between a buzzer and a self-contained power supply, such as a battery. The control terminals of the relay were connected to the power supply of the article in which the alarm system was incorporated, and when the article was connected to a power supply, the relay would be opened and prevent the buzzer from sounding. However, as soon as the article was unplugged in an attempt to remove it from its proper location, the relay would close and the alarm would sound. This approach does not provide a totally satisfactory solution to the problem. For example, if all of the typewriters in a large office incorporated such an alarm, the resulting noise that would be generated during a power failure would be unbearable. Furthermore, this type of alarm system is not generally applicable to all types of items to be protected, but can only be utilized with devices that run on electrical power, and must be connected to their power source.
Another approach to the problem of detecting unauthorized removal of an article has been to use a normally closed push-button type switch that is disposed on the bottom of the article. When the article is placed on a desk, for example, the switch would be opened by the weight of the article and would prevent the buzzer from sounding, but would be closed to actuate the alarm once the protected article was lifted off the desk. However, a thief would be able to easily defeat such an alarm system by simply holding the button closed with his finger or a piece of tape while removing the article from the desk.
In view of the disadvantages associated with these approaches, it has been determined that a successful alarm system requires that an alarm indication should be intermittent, i.e., occur only when a contact is closed, and the contact should be closed only when the protected article is lifted or otherwise moved. A position sensitive type of switch best fulfills these requirements. With this in mind, different types of mercury switches, to control the supply of power to a buzzer upon detection of movement of an article, were tried. However, in almost all cases, the mercury switches did not provide fully satisfactory results. It was found that some switches are not sensitive enough, and the article can be easily lifted and carried away without actuating the alarm by exercising a certain amount of caution in the handling of the article. Other sources were found to be too sensitive, and caused too many false alarms. For example, when the alarm system is incorporated in a typewriter, the vibration imparted to the typewriter during normal use was sufficient to cause the mercury switch to actuate the alarm.
The type of switch that has been found to best meet the requirements of the present invention is a motion and tilt responsive pendulum switch, i.e., a switch that includes a suspended contact or contact actuator. This type of switch is insensitive to short term impact such as that occurring during the striking of typewriter keys or closing of a desk drawer, is responsive to a small degree of tilt and is sensitive to motion, due to the inertia of the suspended contact.
Pendulum type switches have been used in alarm systems in the past. See, for example, U.S. Pat. No. 3,772,645. However, another feature of the present invention that distinguishes it from prior art alarm systems such as the one shown in that patent relates to specific details of the switch and the manner in which the components forming the system are packaged. More specifically, the overall packaging of the alarm system is significant in that it determines the susceptibility of the system to being disabled or otherwise tampered with. For example, if the packaging of the alarm system permits unauthorized disconnection of the power supply from the alarm indicator without actuating the motion sensitive switch, the alarm system will be ineffective for its intended purpose. In addition, the means for disarming, or deactuating, the alarm system must not be easily susceptible to unauthorized use.
It is therefore a general object of the present invention to provide a novel alarm system that produces an audible or visible indication upon detection of the unauthorized movement of an article to be protected.
It is another object of the present invention to provide such an alarm system that is responsive to unauthorized movement of an article but does not produce false alarm indications in response to vibrations caused by ordinary use of the article.
It is a further object of the present invention to provide such an alarm system that is capable of being utilized in a variety of different applications.
It is yet another object of the present invention to provide a novel alarm system that is relatively simple and inexpensive, and therefore not limited to practical use with only expensive items.
It is still another object of the present invention to provide a novel alarm system that is packaged in a manner which inhibits unauthorized disarming of the system.
It is still a further object of the present invention to provide a novel switching system for coded disarmament of an alarm system.
The manner in which the present invention achieves these and other objects and advantages will be apparent from a perusal of the following description of the preferred embodiment of the invention, when taken in conjunction with the accompanying figures.